Inkjet printing is a non-impact method for producing images by the deposition of ink droplets on a substrate (paper, transparent film, fabric, etc.) in response to digital signals. Inkjet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging. In recent years the drop size of inkjet printers has tended to become smaller and smaller, resulting in higher resolution and higher quality prints. The smaller drop size is accompanied by smaller nozzle openings in the inkjet printhead. These smaller nozzle openings are easier to plug and more sensitive to extraneous deposits that can affect both the size and placement accuracy of the inkjet drop.
It has been recognized that there is a need to maintain the ink ejecting nozzles of an inkjet printhead, for example, by periodically cleaning the orifices when the printhead is in use, and/or by capping the printhead when the printer is out of use or is idle for extended periods of time. The capping of the printhead is intended to prevent the ink in the printhead from drying out. There is also a need to prime a printhead before use, to insure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles and also periodically to maintain proper functioning of the orifices. Maintenance and/or priming stations for the printheads of various types of inkjet printers are described in, for example, U.S. Pat. Nos. 4,855,764, 4,853,717 and 4,746,938. Removal of gas from the ink reservoir of a printhead during printing is described in U.S. Pat. No. 4,679,059. In U.S. Pat. No. 4,306,245 to Kasugayama et al., a liquid jet recording device provided with a cleaning protective means for cleaning and protecting an orifice is described. The cleaning protective means is provided at a reset position lying at one end of the scanning shaft of the device.
U.S. Pat. No. 5,128,690 to Nozawa, describes an inkjet apparatus comprising an inkjet head having plural discharge openings for discharging ink. A partial cap member, which can cover at least one of the discharge openings, is connected to a pressure source that can supply sufficient pressure through the covered discharge openings to force any foreign matter into a common liquid chamber. A liquid flow is created in the common chamber to flush the foreign matter from the inkjet head.
U.S. Pat. No. 5,250,962 to Fisher et al., describes a movable priming station for use with an inkjet printer having a printhead with a linear extended array of nozzles. The movable priming station includes a support capable of moving along the extended array of nozzles and a vacuum tube having a vacuum port adjacent to one end thereof. The support is controlled so that the vacuum port does not contact the nozzle-containing surface of the printhead when the support is moved along the linear array of nozzles.
U.K. Patent Application GB2203994 to Takahashi et al., describes an applicator for applying antiwetting compositions to the nozzle bearing face of a printhead of an ink drop printer. The printhead which reciprocates across the face of a platen is moved to one end of the platen where the applicator is placed. The applicator includes an extendable pad which wipes the face of the printhead.
European Patent Application 0263689 to Funk, et al., describes a fluid applicator head in which fluid is to be ejected though a plurality of nozzle orifices by means of pressure pulses or by valve means which control the flow of fluid. The applicator head is flushed out by passing a flushing fluid through the nozzle orifices in which the applicator head is adapted to be moved from a position of applying droplets of fluid to a substrate and to a flushing position at which the nozzle orifices engage with a flushing member so that flushing fluid can flow through the nozzle orifices or conduits associated therewith.
European Patent Application 0621136 to Claflin et al., describes a wet wipe maintenance device for a full width inkjet printer. A shuttle is adapted to travel on a track through a fixed path parallel to an array of nozzle openings defined in a surface of a printhead. Mounted on the shuttle are an applicator for applying a liquid to the nozzle openings and a vacuum device for applying suction to the nozzle openings. The applicator is a wick of urethane felt through which water is supplied.
U.S. Pat. No. 4,306,245 to Kasugayama et al describes a device for cleaning discharge orifices of an inkjet recording head. When the recording head moves to a print scanning region, the recording medium liquid adhering around the discharge orifices is rubbed off by a liquid absorber fitted in a rubbing-off port adjacent to a recovery port.
U.S. Pat. No. 4,306,245 to Kasugayama et al describes an inkjet recorder including a capping mode in which a cap body is brought into contact with a nozzle of a recording head so as to hermetically seal the nozzle. In a recovery mode, the cap body and a vacuum pump communicate with each other to return the recording head to a normally operative condition.
Conventional continuous inkjet printing utilizes electrostatic charging "tunnels" that are placed close to the point where the ink drops are formed in a stream. In this manner, individual drops may be charged, and these drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes known as a "catcher") may be used to intercept the charged drops, while the uncharged drops are free to strike the recording medium. If there is no electric field present, or if the drop break off point is sufficiently far from the electric field (even if a portion of the stream before the drop break off point is in the presence of an electric field), then charging will not occur.
Inks for high-speed inkjet drop printers must have a number of special characteristics. Typically, water-based inks have been used because of their conductivity and viscosity range. Thus, for use in a jet drop printer the ink must be electrically conductive, having a resistivity below about 5000 ohm-cm and preferably below about 500 ohm-cm. For good fluidity through small orifices, the water-based inks generally have a viscosity in the range between 1 and 15 centiposes at 25.degree. C.
Beyond this, the inks must be stable over a long period of time, compatible with inkjet materials, free of microorganisms and functional after printing. Required functional characteristics include resistance to smearing after printing, fast drying on paper, and being waterproof when dried.
Problems to be solved with aqueous inkjet inks include the large energy needed for drying, cockling of large printed areas on paper surfaces, ink sensitivity to rubbing, the need for an anti-microbial agent and clogging of the inkjet printer orifices from dried ink an other adventitious contaminants.
The non-water component of inkjet inks generally serves as a humectant that has a boiling point higher than that of water (100.degree. C). The ink liquid vehicle components, i.e., the water and the humectants, generally possess absorption characteristics on paper and evaporation properties allowing for the desired inkjet printing speed when the ink is to be used in an inkjet printing process.
Many inkjet ink formulations have been patented. U.S. Pat. No. 5,738,716 by Domenic Santilli, et al. issued Apr. 14, 1998 describes the preparation of inkjet inks by dispersing pigments in water.
U.S. Pat. No. 5,431,722 by Yoshiro Yamashita, et al. issued Jul. 11, 1995 discloses the use of a buffer to control the pH of inkjet ink.
U.S. Pat. No. 5,350,616 by Alfred I Pan., et al., issued Sep. 27, 1994 describe nozzle orifices with combined non-wetable and wetable surfaces.
U.S. Pat. No. 5,305,015 Christopher A. Schantz, et al., issued Apr. 19, 1994 ablate nozzle openings from a polyamide film with a laser.
U.S. Pat. No. 5,426,458 Donald E Wenzel., et al., issued Jun. 20, 1995 use poly-p-xylylene films as nozzle orifice surface coatings.
U.S. Pat. No. 5,725,647 James G Carlson., et al., issued Mar. 10, 1998 disclose pigmented inks with added humectants.
An effective cleaning solution for an inkjet print head will have to be compatible with the ink used, and the many limitations on the ink described above.
There remains a need for a simple, economical inkjet printhead cleaning solution that will consistently deliver an accurate and reproducible drop of ink to provide uniform, accurate and consistent prints.